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ext4: avoid race conditions when remounting with options that change dax

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Trying to change dax mount options when remounting could allow mount
options to be enabled for a small amount of time, and then the mount
option change would be reverted.

In the case of "mount -o remount,dax", this can cause a race where
files would temporarily treated as DAX --- and then not.

Cc: stable@kernel.org
Reported-by: syzbot+bca9799bf129256190da@syzkaller.appspotmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2020-06-10 11:16:37 -04:00
parent 68cd44920d
commit 829b37b8cd
1 changed files with 24 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
fs/ext4/super.c
View File

@ -2104,16 +2104,40 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
switch (token) {
case Opt_dax:
case Opt_dax_always:
if (is_remount &&
(!(sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS) ||
(sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_NEVER))) {
fail_dax_change_remount:
ext4_msg(sb, KERN_ERR, "can't change "
"dax mount option while remounting");
return -1;
}
if (is_remount &&
(test_opt(sb, DATA_FLAGS) ==
EXT4_MOUNT_JOURNAL_DATA)) {
ext4_msg(sb, KERN_ERR, "can't mount with "
"both data=journal and dax");
return -1;
}
ext4_msg(sb, KERN_WARNING,
"DAX enabled. Warning: EXPERIMENTAL, use at your own risk");
sbi->s_mount_opt |= EXT4_MOUNT_DAX_ALWAYS;
sbi->s_mount_opt2 &= ~EXT4_MOUNT2_DAX_NEVER;
break;
case Opt_dax_never:
if (is_remount &&
(!(sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_NEVER) ||
(sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS)))
goto fail_dax_change_remount;
sbi->s_mount_opt2 |= EXT4_MOUNT2_DAX_NEVER;
sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS;
break;
case Opt_dax_inode:
if (is_remount &&
((sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS) ||
(sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_NEVER) ||
!(sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_INODE)))
goto fail_dax_change_remount;
sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS;
sbi->s_mount_opt2 &= ~EXT4_MOUNT2_DAX_NEVER;
/* Strictly for printing options */
@ -5454,12 +5478,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
err = -EINVAL;
goto restore_opts;
}
if (test_opt(sb, DAX_ALWAYS)) {
ext4_msg(sb, KERN_ERR, "can't mount with "
"both data=journal and dax");
err = -EINVAL;
goto restore_opts;
}
} else if (test_opt(sb, DATA_FLAGS) == EXT4_MOUNT_ORDERED_DATA) {
if (test_opt(sb, JOURNAL_ASYNC_COMMIT)) {
ext4_msg(sb, KERN_ERR, "can't mount with "
@ -5475,18 +5493,6 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
goto restore_opts;
}
if ((sbi->s_mount_opt ^ old_opts.s_mount_opt) & EXT4_MOUNT_DAX_ALWAYS ||
(sbi->s_mount_opt2 ^ old_opts.s_mount_opt2) & EXT4_MOUNT2_DAX_NEVER ||
(sbi->s_mount_opt2 ^ old_opts.s_mount_opt2) & EXT4_MOUNT2_DAX_INODE) {
ext4_msg(sb, KERN_WARNING, "warning: refusing change of "
"dax mount option with busy inodes while remounting");
sbi->s_mount_opt &= ~EXT4_MOUNT_DAX_ALWAYS;
sbi->s_mount_opt |= old_opts.s_mount_opt & EXT4_MOUNT_DAX_ALWAYS;
sbi->s_mount_opt2 &= ~(EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE);
sbi->s_mount_opt2 |= old_opts.s_mount_opt2 &
(EXT4_MOUNT2_DAX_NEVER | EXT4_MOUNT2_DAX_INODE);
}
if (sbi->s_mount_flags & EXT4_MF_FS_ABORTED)
ext4_abort(sb, EXT4_ERR_ESHUTDOWN, "Abort forced by user");